Method and an apparatus in a ventilation system

ABSTRACT

A method for recovering heat and humidity in a ventilation system includes cooling warm and humid exhaust air at a condensation surface in a heat exchanger and collecting the condensate as formed, heating dry and cold supply air at the opposite side of the condensation surface and atomizing the condensate and supplying the atomized condensate to the supply air at the supply air inlet of the heat exchanger. The atomizing is generated b a piezoelectric atomizer. A device for recovering heat and humidity in a heat exchanger in a ventilation system includes a condensation surface at the exhaust air side of the heat exchanger and a collection device for condensate. At the inlet of the supply air side of the heat exchanger there is provided a piezoelectric atomizer that is fed with the condensate for supplying atomized condensate to the inlet.

BACKGROUND AND SUMMARY

The present invention relates to a method, in a ventilation system, of transferring heat and humidity from departing exhaust air to incoming supply air, and comprises the steps that heat is extracted from the exhaust air in an exhaust air side of a heat exchanger, that the extracted heat is at least partly transferred to the supply air in a supply air side of a heat exchanger, and that humidity carried by the exhaust air is bonded in the exhaust air side and at least partly transferred to the supply air.

The present invention also relates to an apparatus, in a ventilation system, for transferring heat and humidity from departing exhaust air to incoming supply air, and comprises a heat exchanger with a supply air side and an exhaust air side, and means for bonding humidity and at least partly transferring this humidity to the supply air.

In the ventilation of dwellings, use is nowadays almost exclusively made of balanced ventilation where, with the aid of an exhaust air fan, exhaust air is accumulated from the various spaces of the dwelling at a heat exchanger which, with the aid of a supply air fan, is fed with supply air which is taken from outdoors and, after heating in the heat exchanger, is fed to the spaces in the dwelling. If, in such an installation, an outdoor temperature of 0° C. were to prevail and a relative humidity of 80%, this outdoor air contains, in absolute terms, very little water, of the order of magnitude of 4 g/m3. If this outdoor air is then heated to room temperature, for example 22° C., the relative humidity will, after the heating, fall to approx. 20% which is far too low a level.

On the other hand, indoor air at a temperature of 22° and having a 50% relative humidity contains approx. 10 g/m3. If this warm and humid air is cooled to 0° C., this implies that approx. 6 g of water per m3 precipitates as condensate. Normally, this condensate is led off to a vent.

If humidification of the heated outdoor air is to take place, this implies quite a considerable supply of energy, since the water thus supplied must be vaporised by the supply of vaporisation heat.

Heat exchangers are previously known in the art where the partition between the warm and cold side of the heat exchanger is permeable to humidity and, for example, may contain a salt that binds the humidity. The humidity migrates through the wall and is supplied, at least partly, to the supply air.

A heat exchanger of this type cannot be regulated as regards the humidification of the supply air, for which reason major problems may occur in certain weather conditions. Further, the transfer of humidity in a heat exchanger of this type is incomplete as the major part of the condensation takes place in the coldest part of the heat exchanger where the air on the opposite side of the heat exchanger wall due to the low temperature has a bad ability to absorb humidity.

It is desirable to formulate the method intimated by way of introduction so that a humidification of the supply air may take place utilising the thermal content of the exhaust air for vaporisation. It is also desirable to formulate the method so as to ensure good possibilities of accurate regulation of the relative humidity in the supply air, and also in addition good possibilities for cleaning.

It is desirable to design an apparatus so that analogous goals will be attained.

A method according to an aspect of the present invention is characterised in that the humidity is bonded by condensation in the exhaust air side of the heat exchanger, that the precipitated condensate is accumulated, that at least a part of the condensate is atomised to form a mist or aerosol of minute airborne water particles in the liquid phase and is supplied to the supply air in or at the supply air side of the heat exchanger.

An apparatus according to an aspect of the present invention is characterised in that the means for bonding and transferring humidity comprise a condensation surface in the exhaust air side which is cooled by the supply air, accumulation and conduction means for accumulating the condensate, an atomiser for atomising or finely dividing the condensate into a mist or aerosol of minute, airborne water particles in the liquid phase, the accumulation and conduction means being disposed to emit condensate to the atomiser.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings:

FIG. 1 is a schematic view of a prior art heat exchanger;

FIG. 2 shows the heat exchanger according to FIG. 1, but modified according to the present invention; and

FIG. 3 shows a lower region of a slightly modified embodiment of the heat exchanger according to FIG. 2.

DETAILED DESCRIPTION

In FIG. 1, reference numeral 1 relates to a heat exchanger which operates in counter flow and which has an exhaust air side 2 and a supply air side 3. The exhaust air side may also be entitled the warm side of the heat exchanger and the supply air side be entitled its cold side. The exhaust air 4 flows in accordance with the arrows from above and downwards in the Figure from an exhaust air inlet 5 to an exhaust air outlet 6.

Correspondingly, the supply air 7 flows according to the broken line arrows in a direction from beneath from a supply air inlet 8 in an upward direction to a supply air outlet 9. The partition 10 between the exhaust air side 2 and the supply air side 3 consists of or comprises a thermally conductive material, which is gas-tight and impermeable to water, such as copper, aluminium or certain plastics qualities. The wall thickness of the partition is so slight that the wall may be designated a foil.

If it is assumed that the incoming supply air 7 at the supply air inlet 8 is at 0° C. and has a relative humidity of 80%, at least the lower regions of the partition in the Figure will have a temperature in the proximity of 0°. If the incoming exhaust air is then assumed to be at a temperature of 22° C. and has a relatively humidity of approx. 50%, a condensation will take place against the partition 10, at least at its lower regions. As a result, the partition also constitutes a condensation surface, where reference numeral 12 intimates droplets of deposited condensate, i.e. distilled water. At the disclosed humidity and temperature conditions, as much as 6 g of water per m3 of through-flowing exhaust air may be precipitated out in the form of a condensate which is accumulated in an accumulator 11 and which has hitherto traditionally been led off to a vent.

With the above-disclosed temperature and humidity conditions, the air departing from the supply air outlet 9 will be at a temperature in the proximity of 20° C., but will have a relative humidity which has fallen drastically from the original 80% to a level of the order of magnitude of 20%.

In FIG. 2, the heat exchanger according to FIG. 1 has been supplemented for application of the present invention. Corresponding parts and details carry corresponding reference numerals in both Figures.

In the embodiment according to FIG. 1, the accumulator 11 terminates in a vent for accommodating the condensate. In the embodiment according to FIG. 2, there has been provided an atomiser 15 which possesses the property of atomising or finely dividing water in the liquid phase into extremely minute, air-borne particles in the liquid phase.

Thus, the atomiser emits a fine water mist or aerosol 13, where the individual water particles are so small that they do not adhere to those surfaces which the particles may possibly come into contact with, and further the particles remain floating in the air for lengthy periods of time. In addition, the atomiser 15 is in communication with the accumulator 11, so that at least a part of the condensate may be transferred over to the atomiser 15 via its inlet 14. In that the outlet of the atomiser 15 for mist or aerosol 13 is positioned at the inlet 8 to the supply air side 3 of the heat exchanger, the floating water particles in the mist or aerosol 13 will accompany the flow according, to the arrows 7 so that the temperature is gradually raised and so that vaporisation of the minute water particles takes place. In such instance, the vapour generation heat is taken from the heat that is emitted from the exhaust air 4 in the exhaust air side 2 of the heat exchanger.

Given that the atomiser 15 is positioned in the illustrated manner, the process may be controlled in such a manner that no water particles in the liquid phase remain in the supply air 7 at its outlet 9.

As a result, the advantage will be afforded that bacteria cannot be spread into the space in which the supply air is emitted.

The above-disclosed temperature and humidity conditions are representative of a winter climate in southern Sweden. During other annual seasons, there may be a reason not to humidify the incoming outdoor air 7 to the same extent as during the winter climate. For this reason, the communication between the accumulator 11 and the atomiser 15, in particular its inlet 14, is provided with regulator equipment by means of which the flow can be regulated or completely throttled. Correspondingly, the atomiser 15 proper is connected to a regulator system by means of which the emitted quantity of mist or aerosol per unit of time may be governed in response to the relative humidity in the space in which the supply air is emitted.

The atomiser 15 may be of a plurality of different types and include an atomiser nozzle which is supplied with water at high pressure. Another alternative may be to atomise or finely divide incoming water into the relevant mist or aerosol with the aid of compressed air, or with the aid of a rotary disk or a cup. However, the most practical form of atomiser would probably seem to be an atomiser including a piezoelectric plate 16 which is energised with high frequency a.c. voltage.

Regardless of the method of operation of the atomiser 15, it is important that the airborne water particles be minute, less than 100μ, and preferably of the order of magnitude of between 3 and 20μ.

Given that the water with which the atomiser 15 is supplied is a condensate, it is free of dissolved salts such as those that normally occur in mains water. This implies that no precipitation of salt particles in the air can take place, since the condensate is pure distilled water.

FIG. 3 shows, on a larger scale, the lower region of heat exchanger designed with an example of a piezoelectric atomiser 15. In the Figure, the piezoelectric plate has been given reference numeral 16, while its connection terminals to a source of a.c. voltage are not shown. In FIG. 3, the accumulator and conductor means 11 and 14 have further been given a slightly different constructive design than that which is shown in FIG. 2. It will be apparent from FIG. 3 that a level adjustment may take place in the water container 17 which is included in the atomiser 15. In addition, the departing water mist or aerosol is shown by means of the arrows 13.

In order to distribute the departing water mist or aerosol 13 as thoroughly as possible in the entire air flow in the incoming supply air 7, there is provided at the inlet 8 of the supply air side a mist or aerosol distributor 18 which spreads the mist or aerosol and creates turbulence. 

1. In a ventilation system, a method of transferring heat and humidity from departing exhaust air to incoming supply air, comprising: extracting heat from the exhaust air in an exhaust air side in a heat exchanger, at least partly transferring the extracted heat to the supply air in a supply air side of the heat exchanger, bonding humidity carried by the exhaust air in the exhaust air side and at least partly humidity to the supply air, wherein the humidity is bonded by condensation in the exhaust air side of the heat exchanger, accumulating precipitated condensation, and atomizing or finely dividing into a mist or an aerosol at least a part of the condensate and supplying the mist or aerosol to the supply air in or at the supply air side of the heat exchanger.
 2. The method as claimed in claim 1, wherein the mist or aerosol is supplied at the inlet to the supply air side of the heat exchanger.
 3. The method as claimed in claim 1, wherein the water particles of the mist or aerosol are given a size <100μ.
 4. The method as claimed in claim 1, wherein the mist or aerosol is generated by a piezoelectric plate (16) which is held immersed in the condensate and which is driven by means of a high frequency a.c. voltage.
 5. The method as claimed in claim 1, wherein the supply of mist or aerosol is regulated in response to the relative humidity in the space in which the supply air is emitted.
 6. An apparatus, in a ventilation system, for transferring heat and humidity from departing exhaust air to incoming supply air, comprising: a heat exchanged with a supply air side and an exhaust air side, and means for bonding humidity and at least partly transferring same to the supply air, wherein the means for bonding and transferring humidity comprises a condensation surface in the exhaust air side cooled by the supply air, accumulation and conduction means for accumulating the condensate, an atomiser for atomising or finely-dividing the condensate into a mist or aerosol of minute, air-borne water particles in the liquid phase, the accumulation and conduction means being disposed to emit the condensate to the atomiser.
 7. The apparatus as claimed in claim 6, wherein the outlet of the atomiser for mist or aerosol is in flow communication with the inlet region of the supply air side.
 8. The apparatus as claimed in claim 6, wherein the atomiser includes a piezoelectric plate which is in conductive communication with a source of high frequency a.c. voltage.
 9. The apparatus as claimed in claim 6, characterised by a regulator device which, as an input signal, utilises the relative humidity or a parameter representative thereof in that space in which the supply air is emitted, and which is operative to control the operation of the atomiser or the supply of condensate thereto for regulating the relative humidity in that space in which the supply air is emitted, to a level which is perceived by humans as agreeable. 